The present invention relates to a process for producing fibrous mats as the starting material for compression moulded articles, in that fiberized waste materials are mixed with thermoplastic and/or thermoset or thermosetting binders, the mixture is spread onto an air-permeable conveyor belt to form a fleece and the fleece is compressed at elevated temperature and under pressure to give a transportable mat, from which individual moulded articles are produced by compression moulding at temperatures between 180.degree. and 220.degree. C.
In German Patent 2,845,112, the continuously produced mat is separated after compression into individual blanks, which are dimensioned in accordance with the compression moulded article to be produced therefrom. Particular difficulty is caused in the processing of these blanks to compression moulded articles when the latter have deep shaped-out areas, because the starting material cannot absorb tensile forces, so that, on compression moulding, the material can be thinned out and consequently tear as a result of the combined tensile and shear forces. This also applies in the case of other known mats, which are produced e.g. from cellulose or lignocellulose fibres, instead of fiberized waste materials.
In order to be able to produce complicated and deeply shaped moulded articles from such mat blanks, further aids must be used during the moulding process, namely, a stabilizing substrate on which the mat is placed during the moulding process and a stabilizing support placed above the mat blank. Essentially, two ways have been adopted for this purpose, namely, either constructing the two stabilizing layers in elastic or rubber like manner (DE-AS 2,701,480 and 2,759,279) or to use a substantially non-expanding material (DE-AS 2,713,527). In both cases, the stabilizing layers have the function of enclosing the mat blank between them and during the moulding process to supply it into the deep contours of the lower mould, i.e. to ensure a completely satisfactory tightening of the material. In the first case of elastic stabilzing layers, during the moulding process they are elastically expanded, leading to the entrainment of at least the directly adjacent layers of the mat blank as a result of frictional forces. Thus, thinning out can still occur and is accompanied by tearing. In the second case of the largely expansion-free stabilizing layers, a type of sandwich pack is deliberately produced from the two layers and the intermediate mat blank, the mat being largely gripped between the stabilizing layers during the moulding process and follows the movement of the latter due to its fabric-like surface structure. In both cases and, particularly in the case of moulding processes with large strokes, it has been proposed to elastically suspend the upper stabilizing layer, in order to be able to at least absorb the idle stroke of the upper mould of the press, without expanding or stretching the stabilizing layer (e.g. German Patent 3,001,750). Generally, moulding must take place in two-stage form, in that in the first stage working with the aforementioned stabilizing layers, a preform is produced, which roughly has the contour and a generally larger wall thickness. In the second stage, the preform is compression moulded to its final shape.
As a result of these measures, which are essential in the case of complicated compression moulded articles, naturally a complicated apparatus construction arises with a preforming press and a final shaping press. In the case of extremely complicated compression moulded articles, at least one of the preforming moulds, generally the upper mould, must be subdivided into a plurality of elements, in order to be able to successively produce different parts of the mat blank and permit a satisfactory, i.e. substantially tension-free tightening of said blank (DE-AS 2,338,650). In addition, over a period of time, the stabilizing layers are subJect to wear, i.e. become permanently deformed, so that at relatively short intervals of one to two weeks they have to be replaced, which leads to corresponding increases in equipment costs.